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Estimation of Minimally Important Differences and Patient Acceptable Symptom State Scores for the Patient-Reported Outcomes Measurement Information System Pain Interference Short Form in Rheumatoid Arthritis


ACR Open Rheumatol. 2020 May 9.doi: 10.1002/acr2.11141. Online ahead of print.

Patricia Katz 1, Carol L Kannowski 2, Luna Sun 2, Kaleb Michaud 3

Author Information

1 University of California, San Francisco.

2 Eli Lilly and Company, Indianapolis, Indiana.

3 FORWARD, The National Databank for Rheumatic Diseases, Wichita, Kansas, and University of Nebraska Medical Center, Omaha.

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Objective: Studies have supported the validity of the Patient-Reported Outcomes Measurement Information System (PROMIS) Pain Interference (PI) scale in rheumatoid arthritis (RA). Here, we characterize minimally important differences (MIDs) and patient acceptable symptom state (PASS) values.

Methods: PROMIS PI scores were collected in four periods at 6-month intervals from patients with RA (n > 3200 per period). Both anchor- and distribution-based methods estimated MIDs. Anchors were pain comparisons, pain interference, and general health. Time responses for each anchor-response group (four administrations, each with three change periods) were averaged. The mean changes of the "somewhat worse" and "somewhat better" groups were used as estimates for MID for worsening and improvement, respectively. Distribution-based MID analyses used standardized error of measurement (SEM) and SD. PASS was estimated with the question "If your health was to remain for the rest of your life as it has been in the past 48 hours, would this be acceptable?" MIDs and PASS values were also estimated by baseline pain levels.

Results: Anchor-based methods yielded estimates of 1.65 to 1.84 for worsening and -1.29 to -1.73 for improvement. The SEM estimate was 1.84. The PASS estimate for the entire group was 41.6. Substantial differences in MIDs and PASS were noted among baseline pain groups.

Conclusion: The best estimate of a group-level MID was approximately 2 points, similar to MIDs suggested in other conditions. The PASS value for the entire group was almost an SD better than the population mean. Results should enhance use of PROMIS PI in RA by facilitating interpretation of scores and changes.